Renewable energy sources are of increasing importance. They are a means of reducing dependence on oil and they provide a substitute for other fossil fuels. Also, renewable energy resources can provide for basic chemical constituents to be used in other industries, such as chemical monomers for the making of plastics. Biomass is a renewable resource that can supply some of the need for renewables-based chemicals and fuels.
Biomass includes, but is not limited to, lignin, plant parts, fruits, vegetables, plant processing waste, wood chips, chaff, grains, grasses, corn and corn husks, weeds, aquatic plants, hay, recycled and non-recycled paper and paper products, and any cellulose-containing biological material or material of biological origin. The economics of producing oil from biomass depend on the yield of oil produced from a quantity of biomass. When heated in an environment with low or no oxygen, biomass is thermally converted, or pyrolyzed, to generate a liquid known as pyrolysis oil. A modern form of pyrolysis, or rapid thermal conversion, is conducted under moderate temperatures, typically 400° C. to 600° C., and short residence times, such as less than 5 seconds. An example is flash pyrolysis that operates under such conditions and produces a pourable liquid product or pyrolysis oil from the thermal conversion of biomass feedstock or petroleum-based feedstock. Pyrolysis oil thermally converted from biomass feedstock has a higher energy density than the biomass feedstock. Further, the pyrolysis oil thermally converted from biomass feedstock is more easily stored and transported than the biomass feedstock. For economic reasons, it is typically desirable to maximize the yield of pyrolysis oil from the thermal conversion process.
In conventional flash pyrolysis processes, biomass is thermally converted in a reactor during a short contact duration, such as less than about 2 seconds, with a high temperature heat transfer medium, such as a solid heat carrier at about 500° C. This solid heat carrier can be silica sand, low activity catalyst, or other inert material. Typical thermal conversion processes allow oxygen to enter the thermal conversion reactor through the biomass inlet along with the biomass. Further, typical thermal conversion processes utilize equipment or instruments in the reactor system that must be protected from interference by the solid heat carrier or solid product from the thermal conversion of the feedstock. Generally, the instruments are purged with air to dislodge the solid matter or to prevent its intrusion into the instruments. However, the introduction of additional oxygen through the biomass inlet and instrument purge inlets reduces the pyrolysis oil yield proportionally to the amount of oxygen added. As a result, a typical thermal conversion unit exhibits up to about a 2% liquid yield loss due to the ingress of additional oxygen into the thermal conversion reactor.
Accordingly, it is desirable to provide methods and apparatuses for thermally converting biomass with improved pyrolysis oil yield. Further, it is desirable to provide methods and apparatuses for thermally converting biomass which inhibit ingress of oxygen. Also, it is desirable to provide methods and apparatuses for thermally converting biomass which control the oxygen level within a thermal conversion reactor. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.